High-cleaning/low abrasive silica and materials and dentifrice containing such materials

ABSTRACT

Unique abrasive and/or thickening materials that are in situ generated compositions of precipitated silicas and silica gels are provided. Such compositions exhibit different beneficial characteristics depending on the structure of the composite in situ generated material. With low structured composites (as measured via linseed oil absorption levels from 40 to 100 ml oil absorbed/100 g composite), simultaneously high pellicle film cleaning properties and moderate dentin abrasion levels are possible in order to accord the user a dentifrice that effectively cleans tooth surfaces without detrimentally abrading such surfaces. Increased amounts of high structure composite materials tend to accord greater viscosity build and thickening benefits together with such desirable abrasion and cleaning properties, albeit to a lesser extent than for the low structure types. Thus, mid-range cleaning materials will exhibit oil absorption levels from an excess of 100 to 150, and high thickening/low abrasion composite exhibit oil absorption properties in excess of 150. Such an in situ, simultaneously produced precipitated silica/silica gel combination provides such unexpectedly effective low abrasion and high cleaning capability and different thickening characteristics as compared to physical mixtures of such components. Encompassed within this invention is a unique method for making such gel/precipitated silica composite materials for such a purpose, as well as the different materials within the structure ranges described above and dentifrices comprising such.

FIELD OF THE INVENTION

This invention relates to unique abrasive and/or thickening materialsthat are in situ generated compositions of precipitated silicas andsilica gels. Such compositions exhibit different beneficialcharacteristics depending on the structure of the composite in situgenerated material. With low structured composites (as measured vialinseed oil absorption levels from 40 to 100 ml oil absorbed/100 gcomposite), simultaneously high pellicle film cleaning properties andmoderate dentin abrasion levels are possible in order to accord the usera dentifrice that effectively cleans tooth surfaces withoutdetrimentally abrading such surfaces. Increased amounts of highstructure composite materials tend to accord greater viscosity build andthickening benefits together with such desirable abrasion and cleaningproperties, albeit to a lesser extent than for the low structure types.Thus, mid-range cleaning materials will exhibit oil absorption levelsfrom an excess of 100 to 150, and high thickening/low abrasion compositeexhibit oil absorption properties in excess of 150. Such an in situ,simultaneously produced precipitated silica/silica gel combinationprovides such unexpectedly effective low abrasion and high cleaningcapability and different thickening characteristics as compared tophysical mixtures of such components. Encompassed within this inventionis a unique method for making such gel/precipitated silica compositematerials for such a purpose, as well as the different materials withinthe structure ranges described above and dentifrices comprising such.

BACKGROUND OF THE PRIOR ART

An abrasive substance has been included in conventional dentifricecompositions in order to remove various deposits, including pelliclefilm, from the surface of teeth. Pellicle film is tightly adherent andoften contains brown or yellow pigments which impart an unsightlyappearance to the teeth. While cleaning is important, the abrasiveshould not be so aggressive so as to damage the teeth. Ideally, aneffective dentifrice abrasive material maximizes pellicle film removalwhile causing minimal abrasion and damage to the hard tooth tissues.Consequently, among other things, the performance of the dentifrice ishighly sensitive to the extent of abrasion caused by the abrasiveingredient. Conventionally, the abrasive cleaning material has beenintroduced in flowable dry powder form to dentifrice compositions, orvia redispersions of flowable dry powder forms of the polishing agentprepared before or at the time of formulating the dentifrice. Also, andmore recently, slurry forms of such abrasives have been provided tofacilitate storage, transport, and introduction within target dentifriceformulations.

Synthetic low-structure silicas have been utilized for such a purposedue to the effectiveness such materials provide as abrasives, as well aslow toxicity characteristics and compatibility with other dentifricecomponents, such as sodium fluoride, as one example. When preparingsynthetic silicas, the objective is to obtain silicas which providemaximal cleaning with minimal impact to the hard tooth surfaces. Dentalresearchers are continually concerned with identifying abrasivematerials that meet such objectives.

Synthetic silicas (of higher structure) have also been utilized asthickening agents for dentifrices and other like paste materials inorder to supplement and modify the rheological properties for improvedcontrol, such as viscosity build, stand up, brush sag, and the like. Fortoothpaste formulations, for example, there is a need to provide astable paste that can meet a number of consumer requirements, including,and without limitation, the ability to be transferred out of a container(such as a tube) via pressure (i.e., squeezing of the tube) as adimensionally stable paste and to return to its previous state uponremoval of such pressure, the ability to be transferred in such a mannerto a brushhead easily and without flow out of the tube during and aftersuch transference, the propensity to remain dimensionally stable on thebrush prior to use and when applied to target teeth prior to brushing,and the exhibiting of proper mouthfeel for aesthetic purposes, at least,for the benefit of the user.

Generally, dentifrices comprise a majority of a humectant (such assorbitol, glycerin, polyethylene glycol, and the like) in order topermit proper contact with target dental subjects, an abrasive (such asprecipitated silica) for proper cleaning and abrading of the subjectteeth, water, and other active components (such as fluoride-basedcompounds for anticaries benefits). The ability to impart properrheological benefits to such a dentifrice is accorded through the properselection and utilization of thickening agents (such as hydratedsilicas, hydrocolloids, gums, and the like) to form a proper network ofsupport to properly contain such important humectant, abrasive, andanticaries ingredients. It is thus evident that formulating properdentifrice compositions can be rather complex, both from a compoundingstandpoint as well as the number, amount, and type of components presentwithin such formulations. As a result, although it is not a highpriority within the dentifrice industry, the ability to reduce thenumber of such components, or attempt to provide certain components thatmeet at least two of these needed properties could potentially reduceformulation complexity, not to mention potentially reducing the overallmanufacturing costs.

A number of water-insoluble, abrasive polishing agents have been used ordescribed for dentifrice compositions. These abrasive polishing agentsinclude natural and synthetic abrasive particulate materials. Thegenerally known synthetic abrasive polishing agents include amorphousprecipitated silicas and silica gels and precipitated calcium carbonate(PCC). Other abrasive polishing agents for dentifrices have includedchalk, magnesium carbonate, dicalcium phosphate and its dihydrate forms,calcium pyrophosphate, zirconium silicate, potassium metaphosphate,magnesium orthophosphate, tricalcium phosphate, perlite, and the like.

Synthetically-produced precipitated low-structure silicas, inparticular, have been used as abrasive components in dentifriceformulations due to their cleaning ability, relative safeness, andcompatibility with typical dentifrice ingredients, such as humectants,thickening agents, flavoring agents, anticaries agents, and so forth. Asknown, synthetic precipitated silicas generally are produced by thedestabilization and precipitation of amorphous silica from solublealkaline silicate by the addition of a mineral acid and/or acid gasesunder conditions in which primary particles initially formed tend toassociate with each other to form a plurality of aggregates (i.e.,discrete clusters of primary particles), but without agglomeration intoa three-dimensional gel structure. The resulting precipitate isseparated from the aqueous fraction of the reaction mixture byfiltering, washing, and drying procedures, and then the dried product ismechanically comminuted in order to provide a suitable particle size andsize distribution.

The silica drying procedures are conventionally accomplished using spraydrying, nozzle drying (e.g., tower or fountain), wheel drying, flashdrying, rotary wheel drying, oven/fluid bed drying, and the like.

As it is, such conventional abrasive materials suffer to a certainextent from limitations associated with maximizing cleaning andminimizing dentin abrasion. The ability to optimize such characteristicsin the past has been limited generally to controlling the structures ofthe individual components utilized for such purposes. Examples ofmodifications in precipitated silica structures for such dentifricepurposes are described in the art within such publications as U.S. Pat.Nos. 3,967,563, 3,988,162, 4,420,312, and 4,122,161 to Wason, U.S. Pat.Nos. 4,992,251 and 5,035,879 to Aldcroft et al., U.S. Pat. No. 5,098,695to Newton et al., and U.S. Pat. Nos. 5,891,421 and 5,419,888 to McGillet al. Modifications in silica gels have also been described within suchpublications as U.S. Pat. No. 5,647,903 to McGill et al., U.S. Pat. No.4,303,641, to DeWolf, II et al., U.S. Pat. No. 4,153,680, to Seybert,and U.S. Pat. No. 3,538,230, to Pader et al. Such disclosures teachimprovement in such silica materials in order to impart increasedpellicle film cleaning capacity and reductions in dentin abrasion levelsfor dentifrice benefits. However, these typical improvements lack theability to deliver preferred property levels that accord a dentifriceproducer the ability incorporate such an individual material indifferent amounts with other like components in order to effectuatedifferent resultant levels of such cleaning and abrasioncharacteristics. To compensate for such limitations, attempts have beenundertaken to provide various combinations of silicas to permittargeting of different levels. Such silica combinations involvingcompositions of differing particle sizes and specific surface areas aredisclosed in U.S. Pat. No. 3,577,521. to Karlheinz Scheller et al., U.S.Pat. No. 4,618,488 to Macyarea et al., U.S. Pat. No. 5,124,143 toMuhlemann, and U.S. Pat. No. 4,632,826 to Ploger et al. Such resultantdentifrices, however, fail to provide desired levels of abrasion andhigh pellicle cleaning simultaneously.

Another attempt has been made to provide physical mixtures ofprecipitated silicas of certain structures with silica gels, notablywithin U.S. Pat. No. 5,658,553 to Rice. It is generally accepted thatsilica gels exhibit edges, and thus theoretically exhibit the ability toabrade surfaces to a greater degree, than precipitated silicas, even lowstructured types. Thus, the blend of such materials together within thispatent provided, at that time, an improvement in terms of controlled buthigher levels of abrasiveness coupled with greater pellicle filmcleaning ability than precipitated silicas alone. In such a disclosure,it is shown that separately produced and co-incorporated silica gels andprecipitated silicas can permit increased PCR and RDA levels but withapparently greater control for lower abrasive characteristics than forpreviously provided silicas exhibiting very high PCR results.Unfortunately, although these results are certainly a step in the rightdirection, there is still a largely unfulfilled need to provide asilica-based dental abrasive that exhibits sufficiently high pelliclefilm cleaning properties with simultaneously lower radioactive dentinabrasive characteristics such that film removal can be accomplishedwithout deleterious dentin destruction. In effect, the need is for asafer abrasive that exhibits a significantly higher PCR level versus RDAlevel than has previously been provided within the dental silicaindustry. Again, the Rice patent is merely a start toward desirableabrasive characteristics. Furthermore, the requirement to produce theseseparate gel and precipitate materials and meter them out for propertarget levels of such characteristics adds costs and process steps tothe manufacturing procedure. A manner of providing the benefits of suchcombinations, but to a very high level of pellicle film cleaning and ata relatively low to moderate degree of dentin abrasion, withsimultaneous facilitation of incorporation within dentifrice formulationare thus unavailable to the industry at this time.

There is always a desire to limit the number of additives required forpurchase, storage and introduction within dentifrice formulations. Assuch, the ability to provide simultaneous thickening and abrasivecharacteristics to avoid the addition of multiple components for suchproperties is an unmet need within the industry.

OBJECTS AND SUMMARY OF THE INVENTION

It has now been found that modifications in the processes for producingprecipitated silicas can result in the in situ simultaneous productionof targeted amounts of silica gels therein, particularly those in whichthe final structure of the in situ generated composite can becontrolled. Such a novel method thus permits the production of in situgenerated gel/precipitate silica materials that provide excellent dentinabrasion and pellicle film cleaning capabilities within dentifrices or,in the alternative, such formulations that exhibit excellent thickeningproperties as well as desirable abrasive and cleaning properties throughthe introduction of such a singularly produced, stored, and introducedadditive.

In particular, the specific in situ formed composites exhibit very highlevels pellicle film cleaning properties compared with lower radioactivedentin abrasion results such that the resultant materials can be addedwith other abrasive materials (such as lower structure precipitatedsilicas, calcium carbonates, and the like) for the dentifrice producerto target certain high levels of cleaning with lower abrasiveness thusproviding the optimization of cleaning while providing a larger marginof abrasion protection to the ultimate user. It is also believed,without intending to be bound to any specific scientific theory, thatthe increased amount of silica gel within the final composite materialsaids in providing narrower particle size ranges in order to contribute acontrolled result of high cleaning and reduced dentin abrasion levels.As will be discussed in greater detail below, the physically mixedcombination of such materials (i.e., not simultaneously produced withinthe same reaction) has been found to impart limited levels of suchproperties, namely the need to provide materials (particularly aprecipitated silica component) that exhibits an extremely high,potentially deleterious dentin abrasion level in order to impart, at thesame time, an acceptable high pellicle film cleaning level. The novel insitu generated precipitated/gel combination silicas unexpectedly providea higher degree of pellicle film cleaning with a significantly lowerdentin abrasion value, thus according the dentifrice industry not only apotentially more desirable lower abrasive material for better dentalprotection. It has been realized that the presence of varied amounts ofsuch a silica gel component permits the benefit of the sharp edgesexhibited by the gel agglomerates for abrasiveness, with the coexistenceof variable levels of silica precipitates of different structures toaccord an overall composite exhibiting one of three general properties:high cleaning, mid-range cleaning, or thickening/low cleaning. Suchgeneral properties are all dependent upon the structure of the overallgel/precipitate composite, as measured by linseed oil absorption (asnoted previously). When produced in situ, such a resultantgel/precipitate material provides unexpectedly improved properties ascompared with dry blends of such separately produced components. In sucha manner, as one example for the high cleaning variation, it has beenfound that although the pellicle film cleaning level is quite high, infact the resultant dentin abrasion level is limited, thereby impartingan excellent cleaning material without also imparting too high anabrasion level to the target dental substrate.

Alternatively, but by no means any less important, is the ability toproduce materials of silica-based components simultaneously within thesame reaction medium that imparts dentin abrasion and pellicle filmcleaning characteristics (albeit to a lesser degree than for those notedin the previous paragraph) and coexistent thickening properties in orderto accord such beneficial results with a single additive. The ability tocontrol the level of a silica gel in a final composite and/or the targethigh-, medium-, or low-structure of the precipitate component thereinthrough modifications in starting material concentration and/or geland/or precipitate reaction conditions provides the ability to controlthe overall cleaning, abrasive, and/or thickening characteristics of thecomposite itself. Thus, a composite exhibiting greater thickening andreduced but effective pellicle film cleaning characteristic will includeeither higher amounts of silica gel and/or higher amounts ofhigh-structure precipitate such that the overall composite exhibitssufficiently high linseed oil absorption (greater than 150 ml/100 gmaterial) to provide the target desired thickening/low abrasionproperties. Thus, by controlling such silica gel/precipitate productionparameters, it has been found that a single additive can provide thesediverse cleaning, abrasion, and/or thickening properties withoutresorting to multiple additions of potentially expensive and/ordifficult to incorporate materials for the same purpose.

All parts, percentages and ratios used herein are expressed by weightunless otherwise specified. All documents cited herein are incorporatedby reference.

Accordingly, it is one object of the present invention to provide aprecipitated silica and gel silica composite material providing improvedpellicle film cleaning without an unacceptably high correspondingincrease in dentin or enamel abrasion. Another object of the presentinvention is to provide a new method for the production of sucheffective precipitated/gel silica combinations wherein such materialsare produced simultaneously and in situ, thereby permitting the properratios of such materials to be made during production of the materials,rather than during dentifrice production. Also an object of thisinvention is to provide an in situ generated precipitated/gel silicacomposite material wherein the linseed oil absorption levels exhibitedthereby are within one of three ranges: 40 to 100 ml oil absorbed/100 gcomposite material for a very high cleaning material, greater than 100and up to 150 ml/100 g for a mid-range high cleaning material, and inexcess of 150 for a cleaning/thickening/low abrasion material.

Accordingly, this invention encompasses a method for producingsimultaneously silica gels and precipitated silicas, said methodcomprising the sequential steps of

a) admixing a sufficient amount of an alkali silicate and an acidulatingagent together to form a silica gel composition; and without firstwashing, purifying, or modifying said formed silica gel composition,

b) simultaneously introducing to said silica gel composition asufficient amount of an alkali silicate and an acidulating agent to forma precipitated silica, thereby producing a precipitate/gel silicacombination. Encompassed as well within this invention is the product ofsuch a process wherein the silica gel amount present therein is from 5to 80% by volume of the total precipitated/gel silica resultantsimultaneously produced combination. Further encompassed within thisinvention are the composite materials listed above in the three rangesof oil absorption measurements, and dentifrice formulations comprisingsuch materials as well as the product of the inventive process notedabove.

Generally, synthetic precipitated silicas are prepared by admixingdilute alkali silicate solutions with strong aqueous mineral acids underconditions where aggregation to the sol and gel cannot occur, stirringand then filtering out the precipitated silica. The resultingprecipitate is next washed, dried and comminuted to desired size.

Generally, as well, silica gels include silica hydrogels, hydrous gels,aerogels, and xerogels. Silica gels are also formed by reacting alkalisilicate solutions with strong acids or vice-versa, to form a hydrosoland aging the newly formed hydrosol to form the hydrogel. The hydrogelis then washed, dried and comminuted to form the desired materials.

As noted above, the separate production of such materials hashistorically required manufacture of these separate materials, andproper metering of the two together during the incorporation within adentifrice formulation in such a way as to provide the desiredcleaning/abrasion levels thereof.

To the contrary, the inventive method for simultaneous production ofsuch materials permits the producer to target a range of amounts ofsilica gel and precipitated silica components as well as structures ofprecipitated components to impart the desired level of cleaning/abrasionthrough controlled parameters during production, a significantdifference from previous physicals mixtures (i.e., dry blends) of suchmaterials through separate incorporation. Basically, the novel methodentails targeting the amount of silica gel desired and specificallyselecting certain reaction conditions in order to generate such adesired level during amorphous precipitated silica production.

The inventive abrasive compositions are ready-to-use additives in thepreparation of oral cleaning compositions, such as dentifrices,toothpastes, and the like, particularly suited as a raw material in atoothpaste making process. Furthermore, such silica products can beutilized in applications wherein sharp edges and lower abrasiveness maybe desired, such as, without limitation, foam inhibitors within certainformulations, such as, without limitation, automatic dishwashingdetergents. Additional potential uses of such materials include foodcarriers, rubber additives and carriers, cosmetic additives, personalcare additives, plastic antiblocking additives, and pharmaceuticaladditives, without limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical representation of the correlation between dentinabrasion and pellicle film cleaning ratios for a dentifrice compositionfor inventive in situ produced composites of gel/precipitated silica andcomparative physical mixtures of such materials.

FIG. 2 is a graphical representation of the correlation betweenthickening ability and silica gel structure for inventive in situproduced composites of gel/precipitated silica and comparative physicalmixtures of such materials.

FIG. 3 is a graphical representation of the correlation between thevalues of dentin abrasion and pellicle film cleaning measurements for adentifrice composition for inventive in situ produced composites ofgel/precipitated silica and the values of the same measurements forcomparative conventional dental abrasives.

DETAILED DESCRIPTION OF THE INVENTION

The abrasive and/or thickening combinations used in the presentinvention are in-situ formed materials that can be readily formulated ondemand with other ingredients to prepare oral cleaning compositionshaving a high cleaning efficacy without causing undue abrasion on toothsurfaces. The essential as well as optional components of the abrasiveand/or thickening compositions and related methods of making same of thepresent invention are described in more detail below.

General Production Method

The silica compositions of the present invention are prepared accordingto the following two-stage process with a silica gel being formed in thefirst stage and precipitated silica formed in the second stage. In thisprocess, an aqueous solution of an alkali silicate, such as sodiumsilicate, is charged into a reactor equipped with mixing means adequateto ensure a homogeneous mixture, and the aqueous solution of an alkalisilicate in the reactor preheated to a temperature of between about 40°C. and about 90° C. Preferably, the aqueous alkali silicate solution hasan alkali silicate concentration of approximately 3.0 to 35 wt %,preferably from about 3.0 to about 25 wt %, and more preferably fromabout 3.0 to about 15 wt %. Preferably the alkali silicate is a sodiumsilicate with a SiO₂:Na₂O ratio of from about 1 to about 4.5, moreparticularly from about 1.5 to about 3.4. The quantity of alkalisilicate charged into the reactor is about 10 wt % to 80 wt % of thetotal silicate used in the batch. Optionally, an electrolyte, such assodium sulfate solution, may be added to the reaction medium (silicatesolution or water). Next, an aqueous acidulating agent or acid, such assulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and soforth (preferably sulfuric acid), added as a dilute solution thereof(e.g., at a concentration of between about 4 to 35 wt %, more typicallyabout 9.0 to 15.0 wt %) is added to the silicate to form a gel. Once thesilica gel is produced and the pH adjusted to the desired level, such asbetween about 3 and 10, the acid addition is stopped and the gel isheated to the batch reaction temperature, preferably between about 65°C. to about 100° C. It is important to note that after this first stageis completed, the produced silica gel is not modified in any way. Thus,this resultant gel is not washed, purified, cleaned, etc., prior tocommencement of the second stage.

Next, the second stage begins after the gel reaction temperature isincreased, with the simultaneous addition to the reactor of: (1) anaqueous solution of the same acidulating agent previously used and (2)additional amounts of an aqueous solution containing the same species ofalkali silicate as is in the reactor, the aqueous solution beingpreheated to a temperature of about 65° C. to about 100° C. The rate ofacidulating agent and silicate additions can be adjusted to control thesimultaneous addition pH during the second stage reaction. This pHcontrol can be used to control product physical properties, generallywith higher average batch pH providing lower structure silica productsand relatively lower average batch pH providing higher structure silicaproducts. High shear recirculation may be utilized, and the acidsolution addition continues until the reactor batch pH drops to betweenabout 4 to about 9. For purposes of this inventive method, the term“average batch pH” is intended to mean the average pH obtained bymeasuring the pH level every 5 minutes during the precipitate formationstage and averaging the total aggregate over total time elapsed.

After the inflows of the acidulating agent and the alkali silicate arestopped, the reactor batch allowed to age or “digest” for between 5minutes to 30 minutes, with the reactor contents being maintained at aconstant pH. After the completion of digestion, the reaction batch isfiltered and washed with water to remove excess by-product inorganicsalts until the wash water from the silica filter cake results in atmost 5% salt byproduct content as measured by conductivity.

The silica filter cake is slurried in water, and then dried by anyconventional drying techniques, such as spray drying, to produce anamorphous silica containing from about 3 wt % to about 50 wt % ofmoisture. The silica may then be milled to obtain the desired medianparticle size of between about 3 μm to 25 μm, preferably between about 3μm to about 20 μm. Classification of even narrower median particle sizeranges may aid in providing increased cleaning benefits as well.

In addition to the above-described production process methodologies ofprecipitating the synthetic amorphous silicas, the preparation of thesilica products is not necessarily limited thereto and it also can begenerally accomplished in accordance with the methodologies described,for example, in prior U.S. Pat. Nos. 3,893,840, 3,988,162, 4,067,746,4,340,583, and 5,891,421, all of which are incorporated herein byreference, as long as such methods are appropriately modified toincorporate recirculation and high shear treatments. As will beappreciated by one skilled in the art, reaction parameters which affectthe characteristics of the resultant precipitated silica include: therate and timing at which the various reactants are added; the levels ofconcentration of the various reactants; the reaction pH; the reactiontemperature; the agitation of the reactants during production; and/orthe rate at which any electrolytes are added.

Alternative methods of production for this inventive material include inslurry form such as, without limitation, procedures taught within U.S.Pat. No. 6,419,174, to McGill et al., as well as filter press slurryprocesses as described within and throughout U.S. Published Pat. Appl.No. 20030019162 to Huang.

The inventive silica composite materials may be characterized andseparated, as discussed above, into three distinct categories, dependentupon the linseed oil absorption ranges exhibited within each. The oilabsorption test, discussed in greater detail below, is generally used todetermine structures of precipitated silica materials as set forth in J.Soc. Cosmet. Chem., 29, 497-521 (August 1978), and Pigment Handbook:Volume 1, Properties and Economics, 2^(nd) ed., John Wiley & Sons, 1988,p. 139-159. For this invention, however, it is important to note thatsuch a test has now been utilized to determine the structure of theoverall gel/precipitate silica composite instead. Thus, the three basictypes of inventive materials are categorized as defined above, and asdiscussed in the following sections.

The inventive in situ generated composites (also referred to as“combinations”) of silica gel and precipitate are useful for variousfunctions, including, without limitation, three primary types: i)high-cleaning, dental abrasives with correlative lower abrasiveness(with an RDA level of less than 250, for instance) than typicalhigh-cleaning silica-based products; ii) mid-range cleaning dentalabrasives with reduced high cleaning levels (as compared with the highcleaning materials from above), but much lower RDA measurements (at mostabout 150, for instance); and iii) thickening (viscosity-modifying)products that exhibit certain levels of cleaning and abrasiveness (suchas an exhibited PCR of less than 90 and a measured RDA of below 80).Production of each type is based upon different factors, such asreaction conditions (e.g., temperature, agitation/shear, addition ratesof reactants, amount of gel component, and the like), and concentrationsof reactants (e.g., mole ratios of silicate to acid, as one example).These will be further delineated separately below.

High-Cleaning Abrasive Materials

The in situ process of this invention has surprisingly yielded, withselectivity followed in terms of reaction pH, reactant composition,amount of gel component, and, as a result, structure of the resultantgel/precipitate silica composite materials made therefrom, abrasivematerials that exhibit exceedingly high pellicle film cleaningproperties. Such high-cleaning materials may be adjusted to target lowerradioactive dentin abrasion levels without compromising the cleaningbenefits, again, through the production of certain low structuregel/precipitate silica composite materials. Such materials areexemplified below in Examples 4, 6, 7, 11, and 15, at least and show theability to clean without detrimental exaggerated dentin abrasion (withindentifrice formulas 1, 3, and 4, for example). Such products may beutilized as the sole cleaning/abrasive component within a dentifrice or,in one potentially preferred embodiment, may be used as a supplementwith other lower abrasive additives, for targeting an overall cleaningand abrasive level for a dentifrice formulation.

For this high cleaning material, the gel component is present in anamount between 5 and 50% by volume of the ultimately formedgel/precipitate silica composite material (and thus the precipitatedsilica component is present in an amount of from 95 to 50% by volume asa result). Although the amount of gel possible to form a high cleaningmaterial may be as high as 50% of the composite material, preferablysuch an amount is much lower mainly because it was found that the higherthe amount of gel present within a high cleaning material, the greateramount of low structure precipitated silica component required to beproduced during the following phase. Thus, the overall amount of gel tobe produced is preferably relatively low (from 10 to 25%, for instance).Such percentages of gel component actually represent the amount ofsilicate present during the production phases for each different silicamaterial. Thus, a 10% gel measurement reflects the presence of 10% ofthe total silicate reactant volume within the reactor during which thegel is initially made (as one example). Subsequent to initial gelproduction, the remaining 90% silicate reactant volume is used forprecipitated silica component production. It is important to note,however, that upon the initiation of the precipitate formation phase,some of the silicate may actually produce gel, but the determination ofpercentages of each component within the ultimately formed compositematerial does not reflect such a possibility. Thus, the percentagesnoted above are merely best estimates, rather than concretedeterminations of final amounts of components. Such an issue existswithin the remaining in situ gel/precipitate composite materialcategories as well.

Generally, it has been determined that such specific high-cleaningabrasives may be produced through a method of admixing a suitable acidand a suitable silicate starting material (wherein the acidconcentration, in aqueous solution, is from 5 to 25%, preferably from 10to 20%, and more preferably from 10 to 12%, and the concentration of thesilicate starting material is from 4 to 35%, also within an aqueoussolution), to initially form a silica gel. Subsequent to gel formation,sufficient silicate and acid are added (without any appreciable degreeof washing, or other type of purification, or physical modification ofthe gel) to the formed gel for further production of varying structure(preferably low in structure, but other structures silica products mayresult during manufacturing as long as the overall structure issufficient to accord the necessary levels of pellicle film cleaning)precipitated silica component desired for a high cleaning compositematerial to be formed. The pH of the overall reaction may be controlledanywhere within the range of 3 to 10, with a higher pH desired forlow-structure precipitated silica production. It has been realized thatin order to provide a high cleaning, moderate to low abrasive materialthrough this process, the amount of gel is preferably lower (as notedabove, from 10 to 30% by volume of the composite) and the amount of lowstructure precipitated silica is preferably relatively high (from 90 to70% by volume of the composite). In order to exhibit the proper PCR andRDA levels associated with this category, the resultant gel/silicacomposite material must exhibit a linseed oil absorption of between 40and 100 ml oil/100 g material.

Broadly, the inventive high cleaning gel/precipitated silica combinationgenerally have the following properties: 10% Brass Einlehner hardnessvalues in the range between about 5 and 30 mg loss/100,000 revolutions,and, within a test dentifrice formulation (as presented below within theexamples) RDA (Radioactive Dentin Abrasion) values between about 180 toabout 240, and (within the same test dentifrice formulation) PCR(Pellicle Cleaning Ratio) values of 90 to 160, with a ratio of PCR toRDA within the range of 0.45 to 0.7.

Mid-Range Cleaning Abrasives

The in situ process of this invention has also surprisingly yielded,with similar degrees of selectivity followed in terms of reaction pH,reactant concentrations, amount of gel component, and, as a result,overall structure of the resultant gel/precipitate silica compositematerials made therefrom as for the high cleaning materials describedabove, a method for producing a mid-range product (essentially reduced,but still relatively high, cleaning levels with lower abrasion levels)composites as well. Thus, selection of differing concentrations, pHlevels, ultimate gel proportions, among other things, can producegel/precipitate silica composite materials of overall medium structuresin order to accord relatively high pellicle film cleaning results, withlower abrasive properties as compared with the high cleaning materialsdescribed above. Examples 5, 10, 12, 14, 16, and 17, at least, belowshow certain methods of producing such mid-range abrasive products (andfurther exemplified within dentifrice formulations 2, 7, 9, and 10,below).

For this mid-range cleaning material, the gel component is present in anamount between 10 and 60% by weight of the ultimately formedgel/precipitate silica composite material (and thus the precipitatedsilica component is present in an amount of from 90 to 40% by weight asa result). Although the amount of gel possible to form a high cleaningmaterial may be as high as 60% of the composite material, preferablysuch an amount is much lower mainly because it was found that the higherthe amount of gel present within a mid-range cleaning material, thegreater amount of low structure precipitated silica component requiredto be produced during the following phase. Thus, the overall amount ofgel to be produced is preferably relatively low (from 20 to 33%, forinstance). Such percentages of gel component actually represent theamount of silicate present during the production phases for eachdifferent silica material, as described above for the high cleaningmaterial.

Generally, it has been determined that such specific mid-range cleaningabrasives may be produced through a method of admixing a suitable acidand a suitable silicate starting material (wherein the acidconcentration, in aqueous solution, is from 5 to 25%, preferably from 10to 20%, and more preferably from 10 to 12%, and the concentration of thesilicate starting material is from 4 to 35%, also within an aqueoussolution), to initially form a silica gel. Subsequent to gel formation,sufficient silicate and acid are added (without any appreciable degreeof washing, or other type of purification, or physical modification ofthe gel) to the formed gel for further production of appropriatelystructured precipitated silica component desired for a mid-rangecleaning composite material to be formed. The pH of the overall reactionmay be controlled anywhere within the range of 3 to 10. Depending on theamount of gel initially formed, the amount and structure of precipitatedsilica component may be targeted in much the same way as for the highcleaning material. It has been realized that in order to provide amid-range cleaning, low abrasive material through this process, ascompared with the high cleaning materials noted above, the amount of gelis preferably higher (as noted above, from 10 to 60% by volume of thecomposite, preferably from 20 to 33%) and the amount of low structureprecipitated silica is preferably lower (from 90 to 40% by volume of thecomposite, preferably from 80 to 67%). In order to exhibit the properPCR and RDA levels associated with this category, the resultantgel/silica composite material must exhibit a linseed oil absorption ofgreater than 100 up to 150 ml oil/100 g material.

Broadly, the inventive mid-range cleaning gel/precipitated silicacombination generally have the following properties: 10% Brass Einlehnerhardness values in the range between 2.5 and 12.0, and, within a testdentifrice formulation (as presented below within the examples) RDA(Radioactive Dentin Abrasion) values between about 95 to about 150, and(within the same test dentifrice formulation) PCR (Pellicle CleaningRatio) values of 90 to 120, with a ratio of PCR to RDA within the rangeof 0.7 to 1.1.

Thickening Cleaners/Abrasives

Lastly, again, in much the manner as the two above types of abrasives,it has surprisingly been found that silica-based viscosity-modifyingmaterials may be provided that also exhibit a certain degree ofabrasiveness and cleaning through the utilization of the inventive insitu process. The presence of a simultaneously produced gel/precipitateappears to surprisingly accord a certain abrasive property within amaterial that, when produced via a high structure silica productionmethod, provides an effective thickening (or other type of viscositymodification) within dentifrice formulations. In such a manner, such athickening agent may be added not only for its viscosity-modifyingeffect, but also to supplement simultaneously present higher cleaningand/or abrasive dentifrice components. Examples 3, 8, 9, and 13, atleast, provide a showing of general methods of producing such thickeningabrasives (and further exemplified within dentifrice formulations 5, 6,and 8, below).

For this low cleaning level material, the gel component is present in anamount between 20 and 85% by volume of the ultimately formedgel/precipitate silica composite material (and thus the precipitatedsilica component is present in an amount of from 80 to 15% by volume asa result, with such a component preferably present in a high structureform). Although the amount of gel possible to form a high cleaningmaterial may be as low as 20% of the composite material, preferably suchan amount is much higher mainly because it was found that the lower theamount of gel present within a thickening abrasive material, the greateramount of high structure precipitated silica component required to beproduced during the following phase. Thus, the overall amount of gel tobe produced is preferably relatively high (from 45 to 65%, 50% morepreferably, for instance). Such percentages of gel component actuallyrepresent the amount of silicate present during the production phasesfor each different silica material, as described above for the othercategories of cleaning materials.

Generally, it has been determined that such specific thickeningabrasives may be produced through a method of admixing a suitable acidand a suitable silicate starting material (wherein the acidconcentration, in aqueous solution, is from 5 to 25%, preferably from 10to 20%, and more preferably from 10 to 12%, and the concentration of thesilicate starting material is from 4 to 35%, also within an aqueoussolution), to initially form a silica gel. Subsequent to gel formation,sufficient silicate and acid are added (without any appreciable degreeof washing, or other type of purification, or physical modification ofthe gel) to the formed gel for further production of high structureprecipitated silica component desired for a thickening abrasivecomposite material to be formed. The pH of the overall reaction may becontrolled anywhere within the range of 3 to 10. Depending on the amountof gel initially formed, the amount and structure of precipitated silicacomponent may be targeted by reacting the subsequent silicate and acidreactants within a more acidic medium to form greater amounts of highstructure precipitated silica components. It has been realized that inorder to provide a thickening abrasive material through this process,the amount of gel is preferably higher (as noted above, from 20 to 85%by volume of the composite, preferably from 45 to 65%) and the amount oflow structure precipitated silica is preferably relatively low (as lowas possible), while the amount of high structure precipitated silica ispreferably relatively high (from 80 to 15% by volume of the composite,preferably from 55 to 35%). In order to exhibit the proper PCR and RDAlevels associated with this category, the resultant gel/silica compositematerial must exhibit a linseed oil absorption of greater than 150,possibly with a maximum of about 225 ml oil/100 g material.

Broadly, the inventive thickening abrasive gel/precipitated silicacombination generally have the following properties: 10% Brass Einlehnerhardness values in the range between 1.0 and 5.0 mg loss/100,000revolutions, and, within a test dentifrice formulation (as presentedbelow within the examples) RDA (Radioactive Dentin Abrasion) valuesbetween about 20 to about 80, and (within the same test dentifriceformulation) PCR (Pellicle Cleaning Ratio) values of about 50 to 80,with a ratio of PCR to RDA within the range of 0.8 to 3.5.

Dentifrice Uses of the Inventive Materials

The inventive in situ generated gel/precipitate silica compositematerials described herein may be utilized alone as the cleaning agentcomponent provided in the dentifrice compositions of this invention,although, at least for the high cleaning category materials, themoderately high RDA levels may be unacceptable to some consumers. Thus,a combination of the inventive composite materials with other abrasivesphysically blended therewith within a suitable dentifrice formulation ispotentially preferred in this regard in order to accord targeted dentalcleaning and abrasion results at a desired protective level. Thus, anynumber of other conventional types of abrasive additives may be presentwithin inventive dentifrices in accordance with this invention. Othersuch abrasive particles include, for example, and without limitation,precipitated calcium carbonate (PCC), ground calcium carbonate (GCC),dicalcium phosphate or its dihydrate forms, silica gel (by itself, andof any structure), amorphous precipitated silica (by itself, and of anystructure as well), perlite, titanium dioxide, calcium pyrophosphate,hydrated alumina, calcined alumina, insoluble sodium metaphosphate,insoluble potassium metaphosphate, insoluble magnesium carbonate,zirconium silicate, aluminum silicate, and so forth, can be introducedwithin the desired abrasive compositions to tailor the polishingcharacteristics of the target formulation (dentifrices, for example,etc.), if desired, as well.

The precipitate/gel silica combination described above, whenincorporated into dentifrice compositions, is present at a level of fromabout 5% to about 50% by weight, more preferably from about 10% to about35% by weight, particularly when the dentifrice is a toothpaste. Overalldentifrice or oral cleaning formulations incorporating the abrasivecompositions of this invention conveniently can comprise the followingpossible ingredients and relative amounts thereof (all amounts in wt %):

Dentifrice Formulation Ingredient Amount Liquid Vehicle: humectant(s)(total)  5-70 deionized water  5-70 binder(s) 0.5-2.0 anticaries agent0.1-2.0 chelating agent(s) 0.4-10  silica thickener*  3-15 surfactant(s)0.5-2.5 abrasive 10-50 sweetening agent <1.0 coloring agents <1.0flavoring agent <5.0 preservative <0.5

In addition, as noted above, the inventive abrasive could be used inconjunction with other abrasive materials, such as precipitated silica,silica gel, dicalcium phosphate, dicalicum phosphate dihydrate, calciummetasilicate, calcium pyrophosphate, alumina, calcined alumina, aluminumsilicate, precipitated and ground calcium carbonate, chalk, bentonite,particulate thermosetting resins and other suitable abrasive materialsknown to a person of ordinary skill in the art.

In addition to the abrasive component, the dentifrice may also containone or more organoleptic enhancing agents. Organoleptic enhancing agentsinclude humectants, sweeteners, surfactants, flavorants, colorants andthickening agents, (also sometimes known as binders, gums, orstabilizing agents),

Humectants serve to add body or “mouth texture” to a dentifrice as wellas preventing the dentifrice from drying out. Suitable humectantsinclude polyethylene glycol (at a variety of different molecularweights), propylene glycol, glycerin (glycerol), erythritol, xylitol,sorbitol, mannitol, lactitol, and hydrogenated starch hydrolyzates, aswell as mixtures of these compounds. Typical levels of humectants arefrom about 20 wt % to about 30 wt % of a toothpaste composition.

Sweeteners may be added to the toothpaste composition to impart apleasing taste to the product. Suitable sweeteners include saccharin (assodium, potassium or calcium saccharin), cyclamate (as a sodium,potassium or calcium salt), acesulfane-K, thaumatin, neohisperidindihydrochalcone, ammoniated glycyrrhizin, dextrose, levulose, sucrose,mannose, and glucose.

Surfactants are used in the compositions of the present invention tomake the compositions more cosmetically acceptable. The surfactant ispreferably a detersive material which imparts to the compositiondetersive and foaming properties. Suitable surfactants are safe andeffective amounts of anionic, cationic, nonionic, zwitterionic,amphoteric and betaine surfactants such as sodium lauryl sulfate, sodiumdodecyl benzene sulfonate, alkali metal or ammonium salts of lauroylsarcosinate, myristoyl sarcosinate, palmitoyl sarcosinate, stearoylsarcosinate and oleoyl sarcosinate, polyoxyethylene sorbitanmonostearate, isostearate and laurate, sodium lauryl sulfoacetate,N-lauroyl sarcosine, the sodium, potassium, and ethanolamine salts ofN-lauroyl, N-myristoyl, or N-palmitoyl sarcosine, polyethylene oxidecondensates of alkyl phenols, cocoamidopropyl betaine, lauramidopropylbetaine, palmityl betaine and the like. Sodium lauryl sulfate is apreferred surfactant. The surfactant is typically present in the oralcare compositions of the present invention in an amount of about 0.1 toabout 15% by weight, preferably about 0.3% to about 5% by weight, suchas from about 0.3% to about 2%, by weight.

Flavoring agents optionally can be added to dentifrice compositions.Suitable flavoring agents include, but are not limited to, oil ofwintergreen, oil of peppermint, oil of spearmint, oil of sassafras, andoil of clove, cinnamon, anethole, menthol, thymol, eugenol, eucalyptol,lemon, orange and other such flavor compounds to add fruit notes, spicenotes, etc. These flavoring agents consist chemically of mixtures ofaldehydes, ketones, esters, phenols, acids, and aliphatic, aromatic andother alcohols.

Colorants may be added to improve the aesthetic appearance of theproduct. Suitable colorants are selected from colorants approved byappropriate regulatory bodies such as the FDA and those listed in theEuropean Food and Pharmaceutical Directives and include pigments, suchas TiO₂, and colors such as FD&C and D&C dyes.

Thickening agents are useful in the dentifrice compositions of thepresent invention to provide a gelatinous structure that stabilizes thetoothpaste against phase separation. Suitable thickening agents includesilica thickener; starch; glycerite of starch; gums such as gum karaya(sterculia gum), gum tragacanth, gum arabic, gum ghatti, gum acacia,xanthan gum, guar gum and cellulose gum; magnesium aluminum silicate(Veegum); carrageenan; sodium alginate; agar-agar; pectin; gelatin;cellulose compounds such as cellulose, carboxymethyl cellulose,hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxymethylcellulose, hydroxymethyl carboxypropyl cellulose, methyl cellulose,ethyl cellulose, and sulfated cellulose; natural and synthetic clayssuch as hectorite clays; as well as mixtures of these compounds. Typicallevels of thickening agents or binders are from about 0 wt % to about 15wt % of a toothpaste composition.

Therapeutic agents are optionally used in the compositions of thepresent invention to provide for the prevention and treatment of dentalcaries, periodontal disease and temperature sensitivity. Examples oftherapeutic agents, without intending to be limiting, are fluoridesources, such as sodium fluoride, sodium monofluorophosphate, potassiummonofluorophosphate, stannous fluoride, potassium fluoride, sodiumfluorosilicate, ammonium fluorosilicate and the like; condensedphosphates such as tetrasodium pyrophosphate, tetrapotassiumpyrophosphate, disodium dihydrogen pyrophosphate, trisodium monohydrogenpyrophosphate; tripolyphosphates, hexametaphosphates, trimetaphosphatesand pyrophosphates, such as; antimicrobial agents such as triclosan,bisguanides, such as alexidine, chlorhexidine and chlorhexidinegluconate; enzymes such as papain, bromelain, glucoamylase, amylase,dextranase, mutanase, lipases, pectinase, tannase, and proteases;quarternary ammonium compounds, such as benzalkonium chloride (BZK),benzethonium chloride (BZT), cetylpyridinium chloride (CPC), anddomiphen bromide; metal salts, such as zinc citrate, zinc chloride, andstannous fluoride; sanguinaria extract and sanguinarine; volatile oils,such as eucalyptol, menthol, thymol, and methyl salicylate; aminefluorides; peroxides and the like. Therapeutic agents may be used indentifrice formulations singly or in combination at a therapeuticallysafe and effective level.

Preservatives may also be optionally added to the compositions of thepresent invention to prevent bacterial growth. Suitable preservativesapproved for use in oral compositions such as methylparaben,propylparaben and sodium benzoate may be added in safe and effectiveamounts.

The dentifrices disclosed herein may also a variety of additionalingredients such as desensitizing agents, healing agents, other cariespreventative agents, chelating/sequestering agents, vitamins, aminoacids, proteins, other anti-plaque/anti-calculus agents, opacifiers,antibiotics, anti-enzymes, enzymes, pH control agents, oxidizing agents,antioxidants, and the like

Water provides the balance of the composition in addition to theadditives mentioned. The water is preferably deionized and free ofimpurities. The dentifrice will usually comprise from about 20 wt % toabout 35 W % of water.

Useful silica thickeners for utilization within such a toothpasteformulation include, as a non-limiting example, an amorphousprecipitated silica such as ZEODENT® 165 silica. Other preferred (thoughnon-limiting) silica thickeners are ZEODENT® 163 and/or 167 andZEOFREE®153, 177, and/or 265 silicas, all available from J. M. HuberCorporation, Havre de Grace Md., U.S.A.

For purposes of this invention, a “dentifrice” has the meaning definedin Oral Hygiene Products and Practice, Morton Pader, Consumer Scienceand Technology Series, Vol. 6, Marcel Dekker, NY 1988, p. 200, which isincorporated herein by reference. Namely, a “dentifrice” is “ . . . asubstance used with a toothbrush to clean the accessible surfaces of theteeth. Dentifrices are primarily composed of water, detergent,humectant, binder, flavoring agents, and a finely powdered abrasive asthe principal ingredient . . . a dentifrice is considered to be anabrasive-containing dosage form for delivering anti-caries agents to theteeth.” Dentifrice formulations contain ingredients which must bedissolved prior to incorporation into the dentifrice formulation (e.g.anti-caries agents such as sodium fluoride, sodium phosphates, flavoringagents such as saccharin).

The various silica and toothpaste (dentifrice) properties describedherein were measured as follows, unless indicated otherwise.

The Brass Einlehner (BE) Abrasion test used to measure the hardness ofthe precipitated silicas/silica gels reported in this application isdescribed in detail in U.S. Pat. No. 6,616,916, incorporated herein byreference, involves an Einlehner AT-1000 Abrader generally used asfollows: (1) a Fourdrinier brass wire screen is weighed and exposed tothe action of a 10% aqueous silica suspension for a fixed length oftime; (2) the amount of abrasion is then determined as milligrams brasslost from the Fourdrinier wire screen per 100,000 revolutions. Theresult, measured in units of mg loss, can be characterized as the 10%brass Einlehner (BE) abrasion value.

The oil absorption values are measured using the rubout method. Thismethod is based on a principle of mixing linseed oil with a silica byrubbing with a spatula on a smooth surface until a stiff putty-likepaste is formed. By measuring the quantity of oil required to have apaste mixture which will curl when spread out, one can calculate the oilabsorption value of the silica—the value which represents the volume ofoil required per unit weight of silica to saturate the silica sorptivecapacity. A higher oil absorption level indicates a higher structure ofprecipitated silica; similarly, a low value is indicative of what isconsidered a low-structure precipitated silica. Calculation of the oilabsorption value was done as follows: $\begin{matrix}{{{Oil}\quad{absorption}} = {\frac{{ml}\quad{oil}\quad{absorbed}}{{{weight}\quad{of}\quad{silica}},{grams}} \times 100}} \\{= {{ml}\quad{oil}\text{/}100\quad{gram}\quad{silica}}}\end{matrix}$

As a first step in measuring refractive index (“RI”) and degree of lighttransmission, a range of glycerin/water stock solutions (about 10) wasprepared so that the refractive index of these solutions lies between1.428 and 1.46. The exact glycerin/water ratios needed depend on theexact glycerin used and is determined by the technician making themeasurement. Typically, these stock solutions will cover the range of 70wt % to 90 wt % glycerin in water. To determine Refractive index, one ortwo drops of each standard solution is separately placed on the fixedplate of a refractometer (Abbe 60 Refractometer Model 10450). Thecovering plate is fixed and locked into place. The light source andrefractometer are switched on and the refractive index of each standardsolution is read.

Into separate 20-ml bottles, accurately weighed was 2.0+/−0.01 ml of theinventive gel/precipitate silica product and added was 18.0+/−0.01 ml ofeach respective stock glycerin/water solution (for products withmeasured oil absorption above 150, the test used 1 g of inventivegel/precipitate silica product and 19 g of the stock glycerin/watersolution). The bottles were then shaken vigorously to form silicadispersion, the stoppers were removed from the bottles, and the bottleswere placed in a desiccator, which was then evacuated with a vacuum pump(about 24 inches Hg).

The dispersions were then de-aerated for 120 minutes and visuallyinspected for complete de-aeration. The % Transmittance (“%T”) at 590 nm(Spectronic 20 D+) was measured after the samples returned to roomtemperature (about 10 minutes), according to the manufacturer'soperating instructions.

The % Transmittance was measured on the inventive product/glycerin/waterdispersions by placing an aliquot of each dispersion in a quartz cuvetteand reading the % T at 590 nm wavelength for each sample on a 0-100scale. The % Transmittance vs. RI of the stock solutions used wasplotted on a curve. The Refractive index of the inventive product wasdefined as the position of the plotted peak maximum (the ordinate orX-value) on the % Transmittance vs. the RI curve. The Y-value (orabscissa) of the peak maximum was the % Transmittance.

The surface area of the precipitated silica/silica gel reported hereinis determined by the BET nitrogen adsorption method of Brunaur et al.,J. Am. Chem. Soc., 60, 309 (1938).

The total pore volume (Hg) is measured by mercury porosimetry using aMicromeritics Autopore II 9220 apparatus. The pore diameters can becalculated by the Washburn equation employing a contact angle Theta (θ)equal to 140° and a surface tension gamma equal to 485 dynes/cm. Thisinstrument measures the void volume and pore size distribution ofvarious materials. Mercury is forced into the voids as a function ofpressure and the volume of the mercury intruded per gram of sample iscalculated at each pressure setting. Total pore volume expressed hereinrepresents the cumulative volume of mercury intruded at pressures fromvacuum to 60,000 psi. Increments in volume (cm³/g) at each pressuresetting are plotted against the pore radius or diameter corresponding tothe pressure setting increments. The peak in the intruded volume versuspore radius or diameter curve corresponds to the mode in the pore sizedistribution and identifies the most common pore size in the sample.Specifically, sample size is adjusted to achieve a stem volume of 25-75%in a powder penetrometer with a 5 ml bulb and a stem volume of about 1.1ml. Samples are evacuated to a pressure of 50 μm of Hg and held for 5minutes. Mercury fills the pores from 1.5 to 60,000 psi with a 10 secondequilibrium time at each of approximately 103 data collection points.

Median particle size is determined using a Model LA-930 (or LA-300 or anequivalent) laser light scattering instrument available from HoribaInstruments, Boothwyn, Pa.

Two criteria for describing the tightness of the particle sizedistribution are particle size span ratio and beta values as measuredusing a Horiba laser light scattering instrument. By “particle size spanratio” it is meant the cumulative diameter of the particles in the tenthpercentile (D10) minus the cumulative volume at the ninetieth volumepercentile (D90) divided by the diameter of the particles in thefiftieth volume percentile (D50), i.e. (D10−D90)/D50. A lower span ratioindicates a narrower particle size distribution. By “particle size betavalue” it is meant cumulative diameter of the particles in thetwenty-fifth volume percentile (D25) divided by the diameter of theparticles in the seventy-fifth volume percentile (D75), i.e. D25/D75. Ahigher beta value indicates a narrower particle size distribution.

CTAB external surface area of silica is determined by absorption of CTAB(cetyltrimethylammonium bromide) on the silica surface, the excessseparated by centrifugation and determined by titration with sodiumlauryl sulfate using a surfactant electrode. The external surface of thesilica is determined from the quantity of CTAB adsorbed (analysis ofCTAB before and alter adsorption). Specifically, about 0.5 g of silicais placed in a 250-ml beaker with 100.00 ml CTAB solution (5.5 g/L),mixed on an electric stir plate for 1 hour, then centrifuged for 30minutes at 10,000 rpm. One ml of 10% Triton X-100 is added to 5 ml ofthe clear supernatant in a 100-ml beaker. The pH is adjusted to 3.0-3.5with 0.1 N HCl and the specimen is titrated with 0.0100 M sodium laurylsulfate using a surfactant electrode (Brinkmann SUR1501-DL) to determinethe endpoint.

The % 325 mesh residue of the inventive silica is measured utilizing aU.S. Standard Sieve No. 325, with 44 micron or 0.0017 inch openings(stainless steel wire cloth) by weighing a 10.0 gram sample to thenearest 0.1 gram into the cup of the 1 quart Hamilton mixer Model No.30, adding approximately 170 ml of distilled or deionized water andstirring the slurry for at least 7 min. Transfer the mixture onto the325 mesh screen; wash out the cup and add washings onto the screen.Adjust water spray to 20 psi and spray directly on screen for twominutes. (Spray head should be held about four to six inches above thescreen cloth. Wash the residue to one side of the screen and transfer bywashing into an evaporating dish using distilled or deionized water froma washing bottle. Let stand for two to three minutes and decant theclear water. Dry (convection oven @ 150° C. or under infrared oven forapprox. 15 min.) cool and weigh residue on analytical balance.

Moisture or Loss on Drying (LOD) is the measured silica sample weightloss at 105° C. for 2 hours. Loss on ignition (LOI) is the measuredsilica sample weight loss at 900° C. for 2 hours (sample previouslypredried for 2 hours at 105° C.).

The pH values of the reaction mixtures (5 weight % slurry) encounteredin the present invention can be monitored by any conventional pHsensitive electrode.

Sodium sulfate content was measured by conductivity of a knownconcentration of silica slurry. Specifically, 38 g silica wetcake samplewas weighed into a one-quart mixer cup of a Hamilton Beach Mixer, modelNumber 30, and 140 ml of deionized water was added. The slurry was mixedfor 5 to 7 minutes, then the slurry was transferred to a 250-mlgraduated cylinder and the cylinder filled to the 250-ml mark withdeionized water, using the water to rinse out the mixer cup. The samplewas mixed by inverting the graduated cylinder (covered) several times. Aconductivity meter, such as a Cole Palmer CON 500 Model #19950-00, wasused to determine the conductivity of the slurry. Sodium sulfate contentwas determined by comparison of the sample conductivity with a standardcurve generated from known method-of-addition sodium sulfate/silicacomposition slurries.

Further tests followed below were utilized to analyze the structure ofinitially produced silica gel during the overall in situ gel/precipitateproduction method. Included within these analyses was porosity. Such aproperty of accessible porosity was obtained using nitrogenadsorption-desorption isotherm measurements. The BJH(Barrett-Joiner-Halender) model average pore diameter was determinedbased on the desorption branch utilizing an Accelerated Surface Area andPorosimetry System (ASAP 2010) available form Micromeritics InstrumentCorporation, Norcross, Ga. Samples were out-gassed at 150-200° C. untilthe vacuum pressure was about 5 μm of Mercury. Such an analyzer was anautomatic volumetric type at 77 K. Pore volume was obtained at apressure P/P₀=0.99. Average pore diameter is derived from pore volumeand surface area assuming cylindrical pores. Pore size distribution(ΔV/ΔD) was calculated using the BJH method, which provides the porevolume within a range of pore diameters. A Halsey thickness curve typewas used with pore size range of 1.7 to 300.0 nm diameter, with zerofraction of pores open at both ends.

The toothpaste (dentifrice) viscosity is measured utilizing a BrookfieldViscometer Model RVT equipped with a Helipath T-F spindle and set to 5rpm by measuring the viscosity of the toothpaste at 25° C. at threedifferent levels as the spindle descends through the toothpaste testsample and averaging the results. Brookfield viscosity is expressed incentipoise (cP).

The Radioactive Dentin Abrasion (RDA) values of dentifrices containingthe silica compositions used in this invention are determined accordingto the method set forth by Hefferen, Journal of Dental Res., July-August1976, 55 (4), pp. 563-573, and described in Wason U.S. Pat. Nos.4,340,583, 4,420,312 and 4,421,527, which publications and patents areincorporated herein by reference.

The cleaning property of dentifrice compositions is typically expressedin terms of Pellicle Cleaning Ratio (“PCR”) value. The PCR test measuresthe ability of a dentifrice composition to remove pellicle film from atooth under fixed brushing conditions. The PCR test is described in “InVitro Removal of Stain With Dentifrice” G. K. Stookey, et al., J. DentalRes., 61, 1236-9, 1982. Both PCR and RDA results vary depending upon thenature and concentration of the components of the dentifricecomposition. PCR and RDA values are unitless.

PREFERRED EMBODIMENTS OF THE INVENTION

The inventive materials were prepared by sequentially forming (in situ)a first silica gel (or gel-like material) and adding thereto sufficientamounts of reactants to form a precipitated silica component presentsimultaneously with the initially produced gel (or gel-like material).The amount of gel is controlled by the quantity of reactants in thefirst stage while the amount of precipitated silica is controlled by thequantity of reactants in the second stage. The structure of the finalproduct is controlled by the amount of gel first produced as related tothe amount of precipitated silica, as well as reaction parameters, suchas temperature, rates, concentrations, pH, and so forth, as discussed ingreater detail above.

Initial Gel Formation

EXAMPLE 1-2

The first two examples show the initial production of silica gel withinthe overall gel/precipitate production method. After initial production,some of these samples were then washed and purified in order to analyzethe resultant material to determine if an actual gel is first formed aswell as for other gel properties exhibited by such a sample. It isimportant to note that the remainder of the samples was utilized in thefurther production of gel/precipitate products below without anywashing, purifying, etc.

In each example, a volume of aqueous solution of 3.3 mole ratio sodiumsilicate of specified concentration was charged within a 30 gallonreactor and agitated therein at 60 rpm. The reactor contents were thenheated to 50° C. and then 11.4% sulfuric acid (heated to 30° C.) wasadded at a specified rate and for a specified time and the resultantproduct was then allowed to form into a gel-like material. This materialwas then filtered and subsequently washed with water (at about 60° C.)and spray-dried. Such collected and dried material was then tested for anumber of properties as noted below, the tests for which were delineatedabove. The following Table 1 includes reaction parameters andconditions; Table 2 provides analyzed properties for these initiallyproduced gel products. It was evident that, upon analysis, a silica gelmaterial was initially formed. Again, the filtering and washing stepsperformed after collection thereof were only necessary to furtheranalyze the formed gel for certain properties in accordance with Table2, below. Such analysis is not generally performed during the actualinventive in situ production of the target gel/precipitate silicacombination. It was merely an interest to determine if a silica gel hadbeen produced initially and the properties thereof for classificationpurposes. Furthermore, for this table as well as throughout thisdisclosure, any data that was unavailable or unmeasured is representedby dashes. Additionally, it is important to note that the oil absorptionproperties measured for the silica gel alone is not an indication of noris it to be confused with the determination of oil absorption for theentire inventive gel/precipitate silica combination. TABLE 1 ReactionParameters Example No. 1 2 Silicate Conc. % 13 6 Silicate Volume, 1 6060 Acid Addition Rate, lpm 0.47 0.47 Acid Addition Time, min 41.4 24.35Final Reaction pH 9.0 5.28

TABLE 2 Example No. 1 2 % Gel 100 100 % LOD 5.1 10.7 % LOI 5.8 8.00 %325 Mesh Residue 3.3 0.53 5% pH 9.76 6.90 % Na₂SO₄ 3.97 3.18 MPS, μm16.3 10.1 Particle Size Span — 2.10 Particle Size Beta 0.39 0.43 CTAB,m²/g 207 211 BET, m²/g 232 433 BJH Desorption Average 196 37 PoreDiameter (Å) Oil Absorption, ml/100 g 120 81 Pore Volume, cc/g 2.1 1.29BE, mg loss/100,000 rev. 12.73 6.65 RI 1.457 1.451 % T 11 10In Situ Gel/Precipitate Composite Production

EXAMPLES 3-7

Examples 3-7 contained from about 10 to about 23% by volume gel and thusfrom about 90% to about 77% by volume precipitated silica (as noted inthe accompanying tables). The products of these examples had silicastructure levels varying from low structure (LS) to medium structure(MS) to high structure (HS).

A first step was followed in which a volume of aqueous solution ofsodium silicate (Silicate Volume A) of specified concentration (SilicateConcentration A) and a SiO₂:Na₂O ratio of 3.3 was charged within areactor and agitated therein (depending upon the size of the reactor,the agitation speed was from about 60 to about 92 rpm, although anyspeed may be utilized for such a procedure). The reactor contents wereheated to 50° C. and then 11.4% sulfuric acid was added at a specifiedrate (Acid Rate A) for a specified time (Acid Addition Time A). (ForExample 5, for instance, the agitator speed was set to 60 rpm, except itwas increased briefly for 1 minute to 120 RPM during Acid Addition Time4-5 minutes.) At this point, a specified Water Volume, if indicated, wasadded to the formed silica gel. A silica gel was then visuallyrecognized and the pH of the slurry was tested and optionally maintainedat pH 5.0, as indicated, by adjusting the acid addition rate. Theresultant slurry was then heated to as high as 93° C. (with othersheated to lower temperatures, as low as 80° C., but allowed to continueto heat up to 93° C. after the second stage precipitation was started),and such a temperature was then maintained for the duration of the batchproduction. Subsequently, simultaneous addition began of a second amountof an aqueous solution of sodium silicate pre-heated to 85° C. atspecified concentration (Silicate Concentration B) at a specified rate(Silicate Rate B) and the same sulfuric acid at a specified rate (AcidRate B). Recirculation of the reactor contents at a rate of 75 LPM beganafter simultaneous addition of acid and silicate commenced and continuedthrough digestion. After a specified time (Silicate Addition Time B) ofsodium silicate introduction, its flow was stopped. The pH of thereactor contents was continuously monitored during the simultaneousaddition stage. The acid addition continued until the entire batch pHdropped to about 7.0. Once this pH was attained, the acid flow wasslowed to about 2.7 liters per minute and continued at such a rate untilthe overall pH of the resultant batch was dropped to 4.6. The finishedbatch was then heated at 93° C. for 10 minutes (digestion), whilemaintaining the batch pH at 4.6. The resultant slurry was then recoveredby filtration, washed to a sodium sulfate concentration of less thanabout 5% (preferably less than 4%, and most preferably below 2%) asdetermined by monitoring the filtrate conductivity and then spray driedto a level of about 5% water utilizing an inlet temperature of ˜480° C.The dried product was then milled to uniform size. Parameters used forExamples 3-7 are described in Table 3. The Acid rate levels for some ofthe examples were adjusted during the reaction, as noted below. TABLE 3Reaction Parameters Example No. 3 4 5 6 7 Silicate Conc. A, % 6 13 13 1313 Silicate Volume A, l 138 60 60 60 60 Acid Addition Rate A, lpm 5 4.75 4.7 4.7 Acid Addition Time A, min 5 5 5 5 5 Water Volume, liters 0 0150.5 0 0 Reaction pH adjusted to 5.0 Yes No Yes No No Silicate Conc. B,% 14.95 13 17.35 13 13 Silicate Rate B, lpm 9.6 12.8 8.1 12.8 12.8 AcidRate B, lpm 4.6-4.8 4.7 4.7-5.1 4.7 4.7 Silicate Addition Time B, min 4842 48 42 42 Average Simultaneous 4.9 8.1 6.4 8.57 8.0 Addition pH

Several properties of Examples 3-7 were determined according to themethods described above and the results are summarized in Table 4. TABLE4 Example No. 3 4 5 6 7 % Gel 22.9 10 13.4 10 10 Structure HS LS MS LSLS % LOD 6.7 4.9 1.9 5.5 4.5 % LOI 4.4 4.3 4 4.6 3.6 % 325 Mesh 0.4 00.02 0.48 0 Residue 5% pH 6.61 7.47 6.79 7.09 6.53 % Na₂SO₄ 0.35 <.350.74 <.35 0.98 MPS, μm 11.3 7.9 9.5 12.2 4.11 Particle Size Span 1.5 2.21.95 2.12 1.90 Particle Size Beta 0.47 0.26 0.45 0.3 0.46 CTAB, m²/g 24854 147 71 76 BET, m²/g 453 81 252 102 81 Oil Absorption, 168 82 117 7581 ml/100 g Pore Volume, cc/g 2.32 1.66 2.18 1.59 1.59 BE, mg loss/ 3.9818.37 11.4 25.16 7.92 100,000 rev. RI 1.457 — 1.451 1.438 1.441 % T 47 —30 4 10

EXAMPLES 8-12

Examples 8-12 contained about 25-35% by volume gel and about 75-65% byvolume precipitated silica. The products of these examples had silicastructure levels varying from very low structure to high structure.These examples were prepared according to the procedure given in Example3-7, except with the parameters described in Table 5 below (note thatExample 12 was produced within a very large reactor, about 40,000 litersin volume, with an agitation speed of about 92 rpm and a high shearrecirculation flow rate of about 3050 liters/minute). TABLE 5 ReactionParameters Example No. 8 9 10 11 12 Silicate Conc. A, % 6 13 6.0 32.5 13Silicate Volume A, l 200 200 200 60.3 6105 Acid Addition Rate A, lpm 4.74.7 4.7 4.7 191.3 Acid Addition Time A, min 8 16 8 14.1 11.75 WaterVolume, liters 0 0 0 120 0 Reaction pH Adjusted to No No No No No 5.0Silicate Conc. B, % 16.21 13 16.21 13 13 Silicate Rate B, lpm 8.33 12.88.33 12.8 521 Acid Rate B, lpm 4.5-4.7 4.7 4.7-2.0 4.7 191.3 SilicateAddition Time B, 48 31 48 32.9 35.3 min Average Simultaneous 4.34 8.027.1 7.9 — Addition pH

Several properties of Examples 8-12 were determined according to themethods described above and the results are summarized in Table 6. TABLE6 Properties Example 8 9 10 11 12 % Gel 33 33 33 30 25 Structure HS HSMS LS MS % LOD 5.7 5.0 2.0 4.4 7 % LOI 5 3.8 3.3 4.8 4.1 % 325 MeshResidue 0 1.05 0.02 0.11 2 5% pH 6.14 6.96 6.15 8.03 7.52 % Na₂SO₄ 2.240.43 3.97 <0.35 0.82 MPS, μm 10.2 15.5 10.3 12.4 12.6 Particle Size Span1.13 1.96 1.26 — 2.28 Particle Size Beta 0.56 0.37 0.53 0.48 0.3 CTAB,m²/g 318 191 164 50 77 BET, m²/g 522 242 194 84 118 Oil Absorption,ml/100 g 185 167 142 58/53 122 Pore Volume, cc/g 2.97 3.05 2.9 2.64 2.12BE, mg loss/100,000 rev. 1.96 4.27 6.79 18.76 2.94 RI 1.457 1.457 1.4481.438 1.448 % T 57 67 25 6 65.6

EXAMPLES 13-14

Examples 13-14 contained about 50% gel and about 50% precipitatedsilica. The products of these examples had silica structure levelsvarying from low structure to very high structure. These examples wereprepared according to the procedure given in Example 3-7, except withthe parameters described in Table 7 below. TABLE 7 Reaction ParametersExample No. 13 14 Silicate Conc. A, % 13 35 Silicate Volume A, l 30091.2 Acid Addition Rate A, lpm 4.7 4.7 Acid Addition Time A, min 23.523.5 Water Volume, liters 0 209 Reaction pH adjusted to 5.0 No NoSilicate Conc. B, % 13 13 Silicate Rate B, lpm 12.8 12.8 Acid Rate B,lpm 4.71 4.7 Silicate Addition Time B, min 23.5 23.5 AverageSimultaneous Addition pH 7.92 7.29

Several properties of Examples 13-14 were determined according to themethods described above and the results are summarize in Table 8. TABLE8 Example No. 13 14 % Gel 50 50 Structure HS MS % LOD 4.9 4.4 % LOI 3.74.1 % 325 Mesh Residue 0.08 0.07 5% pH 6.75 7.83 % Na₂SO₄ 0.59 1.61 MPS,μm 15.4 10.4 Particle Size Span 1.69 — Particle Size Beta 0.44 0.42CTAB, m²/g 251 90 BET, m²/g 377 127 Oil Absorption, ml/100 g 210 111Pore Volume, cc/g 4.39 1.98 BE, mg loss/100,000 rev. 1.46 6.47 RI 1.4571.441 % T 84 14

EXAMPLES 15-17

Examples 15-17 reflected the ability to adjust the gel level and thesilica structure through pH modifications of the precipitated silicacomponent during gel/precipitate production as well as through changesin reactant concentrations. These examples were prepared according tothe procedure given in Examples 3-12, except with the parametersdescribed in Table 9 below and within the same reactor and under thesame agitation conditions as noted for Example 12, above. Examples 15and 17 had no high shear recirculation, however, whereas Example 16utilized the same high shear recirculation flow rate as Example 12.TABLE 9 Reaction Parameters Example No. 15 16 17 Silicate Conc. A, %13.0 6.0 13.0 Silicate Volume A, l 2442 8140 4884 Acid Addition Rate A,lpm 191.3 191.3 191.3 Acid Addition Time A, min 5 8 11.5 Water Volume,liters 0 0 0 Reaction pH Adjusted to 5.0 No No No Silicate Conc. B, %13.0 16.21 13.0 Silicate Rate B, lpm 521 339 521 Acid Rate B, lpm 191.3191.3 231.7 Silicate Addition Time B, min 42 48 37.6 AverageSimultaneous Addition pH 9.7 7.2 5.4

Several properties of Examples 15-17 were determined according to themethods described above and the results are summarized in Table 10.TABLE 10 Properties Example 15 16 17 % Gel 10 33 20 Structure LS MS MS %LOD 5 2.9 4.1 % LOI 4.3 3.2 4.5 % 325 Mesh Residue 2.6 4.2 0.43 5% pH7.2 6.69 7.17 % Na₂SO₄ 0.59 0.82 0.51 MPS, μm 12.4 13.21 10.35 ParticleSize Span 2.83 2.79 2.52 Particle Size Beta 0.29 0.34 0.41 CTAB, m²/g 92151 185 BET, m²/g 91 166 265 Oil Absorption, ml/100 g 79 115 150 PoreVolume, cc/g 1.39 2.08 2.64 BE, mg loss/100,000 rev. 22.47 5.79 3.83 RI1.432 1.454 1.454 % T 5 67 57Dentifrice Formulations

Toothpaste formulations were prepared using several of theabove-described gel/precipitated silica examples to demonstrate theready-to-use on demand capabilities of the inventive compositionswithout furthering metering of the two components for optimum dentalprotection benefits.

To prepare the dentifrices, the glycerin, sodium carboxymethylcellulose, polyethylene glycol and sorbitol were mixed together andstirred until the ingredients were dissolved to form a first admixture.The deionized water, sodium fluoride, tetrasodium pyrophosphate andsodium saccharin were also mixed together and stirred until theseingredients are dissolved to form a second admixture. These twoadmixtures were then combined with stirring. Thereafter, the optionalcolor was added with stirring to obtain a “pre-mix”. The pre-mix wasplaced in a Ross mixer (Model 130 LDM) and silica thickener, abrasivesilica and titanium dioxide were mixed in without vacuum. A 30-inchvacuum was drawn and the resultant admixture was stirred forapproximately 15 minutes. Lastly, sodium lauryl sulfate and flavor wereadded and the admixture was stirred for approximately 5 minutes at areduced mixing speed. The resultant dentifrice was transferred toplastic laminate toothpaste tubes and stored for future testing. Thedentifrice formulations are given in Table 11 below. The dentifriceformulation utilized was considered a suitable test dentifriceformulation for the purposes of determining PCR and RDA (as well asviscosity) measurements for the inventive and comparative cleaningabrasives. Changes in the amount of carboxymethylcellulose to permitproper formation of the dentifrice from physical and aestheticperspectives were made in certain situations with an offset in theamount of deionized water added, but the overall base dentifriceformulation remained essentially static for the tests followed as notedabove. TABLE 11 Form. Form. 1 Form. 2 Form. 3 Form. 4 Form. 5 Form. 6Form. 7 Form. 8 Form. 9 10 Glycerin 11 11 11 11 11 11 11 11 11 11(99.5%), % Sorbitol 40 40 40 40 40 40 40 40 40 40 (70%), % Deionized 2020.4 20 20.2 20.7 20 20.4 20 20.2 20.7 water, % Carbowax 3 3 3 3 3 3 3 33 3 600¹, % CMC-7MXF², % 1.2 0.8 1.2 1.0 0.5 1.2 0.8 1.2 1.0 0.5Tetrasodium 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 pyrophosphate Sodium0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Saccharin, % Sodium 0.243 0.2430.243 0.243 0.243 0.243 0.243 0.243 0.243 0.243 Fluoride, % Silica 1.51.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 thickener Zeodent ® 165, % Example 420 silica, % Example 5 20 silica, % Example 6 20 silica, % Example 7 20Silica, % Example 8 20 Silica, % Example 9 20 silica, % Example 10 20silica, % Example 13 20 silica, % Example 16 20 Silica, % Example 17 20Silica, % TiO₂, % 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Sodium lauryl1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 sulfate, % Flavor, % 0.65 0.650.65 0.65 0.65 0.65 0.65 0.65 0.65 0.65¹A polyethylene glycol available from the Union Carbide Corporation,Danbury, CT²A carboxymethylcellulose available from the Aqualon division ofHercules Corporation, Wilmington, DE; also acceptable is CEKOL ® 2000, aCMC available from Noviant

The dentifrice formulations prepared above were evaluated for PCR andRDA properties, according to the methods described above; themeasurements, as well as the PCR:RDA ratios for each dentifriceformulation are provided in Table 12 below. The PCR data forFormulations 1, 3, and 8 were obtained from Southeastern Dental ResearchCorporation of Port Allen, La., and the remaining PCR data from OralHealth Research Institute of Indianapolis, Ind. TABLE 12 Form Form 1Form 2 Form 3 Form 4 Form 5 Form 6 Form 7 Form 8 Form 9 10 PCR 123 100153 95 76 64 98 74 97 91 RDA 204 143 233 182 66 73 134 23 117 107 PCR/0.60 0.7 0.65 0.52 1.15 0.88 0.73 3.22 0.83 0.93 RDA

The results show varied performance with highly effective cleaningcapabilities with relatively low dentin abrasion properties.

Several other dentifrice formulations were prepared using a combinationof 2 inventive silicas for Formulations 12-14 and a combination of aninventive silica and a commercial silica (ZEODENT®115 from J.M. HuberCorporation) for Formulation 11. The dentifrice formulations wereprepared according to the method provided above and with much the sameingredients as described above in Table 11. The following Table 13provides the formulas for these toothpastes incorporating blends ofdifferent silica abrasives in relation to the invention describedherein. TABLE 13 Formula Formula Formula Formula 11 12 13 14 Glycerin(99.5%), % 11 11 11 11 Sorbitol (70%), % 40 40 40 40 Deionized water, %20.2 20.6 20.6 20.7 Carbowax 600, % 3 3 3 3 CMC-7MXF, % 1.0 0.6 0.6 0.5Tetrasodium 0.5 0.5 0.5 0.5 pyrophosphate Sodium Saccharin, % 0.2 0.20.2 0.2 Sodium Fluoride, % 0.243 0.243 0.243 0.243 Silica thickener 1.51.5 1.5 1.5 Zeodent ® 165, % Example 5 silica, % 15 0 0 0 Example 7silica, % 0 5 0 0 Example 8 silica, % 0 15 10 6 Example 10 silica, % 0 010 14 ZEODENT ® 115 silica, %¹ 5 0 0 0 TiO₂, % 0.5 0.5 0.5 0.5 Sodiumlauryl sulfate, % 1.2 1.2 1.2 1.2 Flavor, % 0.65 0.65 0.65 0.65¹A low structure precipitated silica available from J.M. HuberCorporation, Havre de Grace, Maryland.

The dentifrice formulations prepared above were evaluated for PCR andRDA properties, according to the methods described above; themeasurements, as well as the PCR:RDA ratios for each dentifriceformulation are provided in Table 14 below. TABLE 14 Formula FormulaFormula Formula 11 12 13 14 PCR 97 90 92 95 RDA 168 96 97 113 PCR/RDA0.58 0.94 0.95 0.84

The cleaning ability of these combinations, in particular Formulas 12,13, and 14, evince a highly surprising and effective dental polishingand film removal material with much lower abrasion levels.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows in graphical representation the ratios of RDA and PCRavailable within some of the dentifrice formulations listed above, ascompared with physical mixtures of silica gel and precipitated silica,produced in much the same way as those disclosed within U.S. Pat. No.5,658,553 to Rice. The slope of each line indicates the general resultsaccorded by each different formulation and shows that the simultaneouslyformed combination of this invention imparts greater PCR results withcorrelated lower RDA. Thus, it has been unexpectedly found that such aninventive combination permits greater cleaning ability withoutsimultaneously unacceptably high dentin abrasion.

All dentifrices exhibited acceptable viscosity, fluoride availability,and excellent aesthetics (stand-up, texture, dispersion). Particularly,in view of the graphical representation within FIG. 1, it is evidentthat the comparative physical blends of such materials do not exhibitthe same desired increase in pellicle film cleaning efficiency withlower RDA values as those of the in situ generated inventioncombinations.

Likewise, in FIG. 2 there is provided a comparison of the thickeningcapabilities of the inventive in situ silica combinations versus thosephysical blends of gels and precipitates described within the Ricepatent (within the same test dentifrice formulation as listed above). Itis evident that there is a significant difference in overall structureand resultant function of these different types of materials as the insitu generated composite materials exhibit differing degrees ofthickening over the spectrum of amounts of gel/precipitate presenttherein than the Rice patent blends. Clearly, then, there is adistinction in form and characteristics for these two different types ofdentifrice additives.

Furthermore, FIG. 3 shows in graphical representation the measurementsof the PCR vs. RDA readings for the inventive gel/precipitate compositematerials over a wide range as compared with the same measurements forthe conventional precipitated silica abrasives (again as measured withinthe same test dentifrice formulation as presented above). It is evidentfrom this representation that the inventive gel/precipitate silicacomposite materials accord much higher PCR results with correlativelower RDA properties than the conventional abrasive materials, showingthe significant differences between the comparative abrasives and theinventive in situ produced types. In this manner, surprisingly, it hasbeen realized that the in situ production of blends of silica gels andprecipitated silica materials provides improved pellicle film cleaningbenefits while simultaneously exhibiting much lower dentin abrasionreadings, thereby providing a more effective cleaning material with alower propensity to deleteriously abrade tooth surfaces during use.

While the invention will be described and disclosed in connection withcertain preferred embodiments and practices, it is in no way intended tolimit the invention to those specific embodiments, rather it is intendedto cover equivalent structures structural equivalents and allalternative embodiments and modifications as may be defined by the scopeof the appended claims and equivalence thereto.

1. An in situ produced gel/precipitate silica combination, wherein saidcombination comprises from 10 to 60% by volume of silica gel, whereinsaid combination exhibits a linseed oil absorption of greater than 100up to 150 ml/100 g, and wherein said combination exhibits a 10% BrassEinlehner hardness value in the range between about 2.5 and 12 mgloss/100,000 revolutions.
 2. The combination of claim 1 wherein saidcombination comprises from 20 to 33% by volume of silica gel.
 3. The insitu produced gel/precipitate silica combination of claim 1 wherein saidcombination is in the form of particles exhibiting a median particlesize range of from 3 to 20 microns.
 4. The in situ producedgel/precipitate silica combination of claim 2 wherein said combinationis in the form of particles exhibiting a median particle size range offrom 3 to 20 microns.
 5. A dentifrice formulation comprising thecombination as defined in claim
 1. 6. A dentifrice formulationcomprising the combination as defined in claim
 2. 7. A dentifriceformulation comprising the combination as defined in claim
 3. 8. Thedentifrice formulation of claim 5 further comprising an abrasivematerial other than said combination.
 9. The dentifrice formulation ofclaim 6 further comprising an abrasive material other than saidcombination.
 10. The dentifrice formulation of claim 7 furthercomprising an abrasive material other than said combination.
 11. Amethod of producing the combination as defined in claim 1, said methodcomprising the sequential steps of a) admixing a sufficient amount of analkali silicate having a concentration of from 4 to 35% within anaqueous solution thereof and an acidulating agent having an acidconcentration within an aqueous solution from 5 to 25% together at atemperature from about 40 to about 90° C. and under agitation to form asilica gel composition; and, without first washing, modifying, orpurifying said formed silica gel composition, b) subsequentlyintroducing to said silica gel composition a sufficient amount of analkali silicate and an acidulating agent to form a precipitated silicawithout affecting the silica gel, thereby producing a gel/precipitatesilica combination, wherein the pH of the overall reaction is within therange of from 3 to
 10. 12. The method of claim 11 wherein the acidconcentration in step “a” is from 10 to 20%.
 13. An in situ producedgel/precipitate silica combination, wherein said combination comprisesfrom 10 to 60% by volume of silica gel, wherein when said combination isintroduced as the sole abrasive component within a test dentifricecomposition said dentifrice composition exhibits a PCR:RDA ratio of fromabout 0.7 to about 1.1, a PCR value between about 90 and 110, and a RDAlevel of between about 95 and about
 150. 14. The combination of claim 13wherein said combination comprises from 20 to 33% by volume of silicagel.
 15. A dentifrice formulation comprising the combination as definedin claim
 13. 16. A dentifrice formulation comprising the combination asdefined in claim
 14. 17. The dentifrice formulation of claim 15 furthercomprising an abrasive material other than said combination.
 18. Thedentifrice formulation of claim 16 further comprising an abrasivematerial other than said combination.
 19. A method of producing thecombination as defined in claim 13, said method comprising thesequential steps of a) admixing a sufficient amount of an alkalisilicate having a concentration of from 4 to 35% within an aqueoussolution thereof and an acidulating agent having an acid concentrationwithin an aqueous solution from 5 to 25% together at a temperature fromabout 40 to about 90° C. and under agitation to form a silica gelcomposition; and, without first washing, modifying, or purifying saidformed silica gel composition, b) subsequently introducing to saidsilica gel composition a sufficient amount of an alkali silicate and anacidulating agent to form a precipitated silica without affecting thesilica gel, thereby producing a gel/precipitate silica combination,wherein the pH of the overall reaction is within the range of from 3 to10.
 20. The method of claim 19 wherein the acid concentration in step“a” is from 10 to 20%.